The present invention relates to containers in general, especially to barrels which consist (either entirely or at least in part) of synthetic thermoplastic material and are produced by blow molding. More particularly, the invention relates to improvements in barrels which can be stacked on top of each other and/or side-by-side to occupy a minimum of space in a vehicle, in storage, on a pallet or on another device which serves for simultaneous transfer of several barrels. Still more particularly, the invention relates to improvements in the design and dimensioning of that end wall of a barrel which is normally the top end wall thereof and has one or more openings for admission and/or evacuation of flowable materials.
It is already known to provide the circumferential wall of a barrel with two flattened portions (hereinafter called flats for short) which render it possible to place several barrels side-by-side so that the flats of neighboring barrels are adjacent to each other. This reduces the space requirements when the barrels are placed in storage, into the van or onto the platform of a vehicle, or onto a pallet or an analogous device for simultaneous transfer of several barrels. As a rule, the flats extend lengthwise of the barrel and may be provided with plane or concave (inwardly bulging) external surfaces. The circumferential wall of the barrel has two domed end portions which taper toward the respective end walls, and the ends of flats normally extend into the respective domed portions of the circumferential wall.
The convexity of the major portions of the circumferential wall enables the barrel to take up substantial stresses when it constitutes the lower or lowermost barrel of a stack of two or more superimposed barrels, i.e., of a stack of barrels which are disposed end-to-end. Such convexity of the major portion of the circumferential wall imparts to the barrel a tendency to bulge outwardly when subjected to axial stresses, i.e., axial stresses cannot cause a cave-in and a resulting collapse of the barrel. As a rule, axial stresses will tend to enlarge the cross-sectional area of the central portion of the barrel, and the thus developing radial stresses are readily taken up by the material of the circumferential wall the major portion of which is curved in the axial as well as in the circumferential direction.
Similar observations apply for the flats. When the top end wall of the barrel carries a heavy load, the resulting axial stresses produce circumferential stresses in the material of the flats, and such circumferential stresses are readily absorbed by the flats, especially by flats whose outer surfaces are concave in the axial as well as in the circumferential direction of the barrel.
Barrels of the just outlined character are produced often by blow molding, in many sizes and shapes, i.e., they range from relatively small casks to large containers with a capacity of up to and in excess of 120 liters. Such containers can be used for storage of liquids and/or granular materials.
A serious drawback of presently known plastic barrels or analogous containers is that they cannot be readily stacked on top of each other without danger of slippage and that they cannot be readily manipulated by attendants or by automatic transfer apparatus.